This application is a continuation-in-part of U.S. patent application Ser. No. 09/879,709, filed Jun. 12, 2001, which claims priority from U.S. Provisional Patent Application Ser. No. 60/215,256, filed Jun. 30, 2000, both of which are hereby incorporated herein by reference. The present invention relates to balls and other welded plastic items. In the process of developing my prior invention relating to balls used inside of tires, and testing it in tires used for off-road motorcycle racing, which is a very rigorous and abusive environment, the balls had various failure modes. One failure mode involved the valves on the balls, and another involved the weld that held the two halves of the ball together.
In the prior art welds of layers of thermoplastic material, the weld is made in a weld area between two flat portions of opposed dies. The dies are energized, and the two layers of material between the dies are melted, merging together to form a single, merged piece. The weld made in that area between the two weld surfaces of the dies is what is relied upon to hold the two layers together. Whenever this process is used, it results in some thinning of the layer material adjacent to the weld. This creates a weak area, which is where the balls failed.
Other failure modes involved the valve that was used to inflate the ball. The valves were made of a material different from the material of the ball, and there were some failures at the weld/seal between the valve and the ball. In addition, the sharp corners of the valves abraded and even pierced the wall of the ball under the severe conditions of off-road motorcycle racing.